In the current market, four-stroke piston reciprocating engines are the ones which are most widely used, but rotary engines are the ones which are well-known but rarely applied.
Just as the conventional reciprocating engines, the rotary engines obtain the rotating force from expansion pressure generated during the combustion of air-fuel mixed gas. The difference between the two types of engines is the use manner of the expansion pressure. In a reciprocating engine, the expansion pressure generated on the top surface of a piston pushes the piston downwards, then mechanical force is transferred to a connecting rod, and a crankshaft is driven to rotate, while in a rotary engine, the expansion pressure is exerted on a side surface of a rotor, and then the rotor is driven to rotate.
Compared with the conventional reciprocating engine, the rotary engine has the advantages that the engine speed is increased, the mass is low, the size is small, the power per liter is high, the operation is smooth, and the vibration and the noise are low.
Triangular rotary engines, taking a great proportion of the conventional rotary engines, are complex in structure, high in production requirements, difficult in cylinder compression ratio adjustment, high in fuel oil consumption, and insufficient in power.